Python 3.5为什么map（）比列表理解慢？

Question

（i5 ivybridge cpu windows 10）地图似乎每次出现都很慢，因为这是一个非常长的列表，它应该做得很好

import time
l = [2049 for i in range(20000000)]
def f(e):
    return (e * 2) - 56

st = time.time()
l = list(map(f,l))
end = time.time()
print ("map: "+str(end-st))

l = [2049 for i in range(20000000)]

st = time.time()
l = [f(e) for e in l]
end = time.time()
print ("list comp: "+str(end-st))

打印：

map: 4.037442207336426
list comp: 3.9109268188476562